Electrical submersible pump assemblies are commonly used in hydrocarbon producing wells to pump well fluid. These assemblies include a rotary pump driven by an electrical motor. A seal section coupled between the pump and motor reduces a pressure differential between well fluid and motor oil or lubricant contained in the motor and part of the seal section. Usually, a string of production tubing supports the submersible pump assembly in the well. A drive shaft extends from the motor through the seal section to the pump.
U.S. Pat. No. 7,431,093 discloses a system employing primary and secondary pumps suspended in a well by a supporting device. The secondary pump is filled with a buffer fluid that is sealed by temporary barriers in the intake ports. The operator runs the primary pump while the secondary pump remains in the stored, non operating mode. Eventually, the primary pump fails, or for other reasons, the operator shuts down the primary pump in order to begin using the secondary pump. The operator uses various techniques to open the temporary barriers and expel the buffer fluid, then supplies power to run the secondary pump.
The secondary pump may be in the stored mode for quite a long time. There is a risk that the barriers and other seals leak, admitting well fluid into the secondary pump, as well as into contact with the motor oil of the secondary motor. The well fluid may be corrosive and cause damage to the pump stages. The well fluid would also damage the internal components of the motor.